Backlight unit and liquid crystal display device having the same

ABSTRACT

A backlight unit for a liquid crystal display (“LCD”) device includes a light emitting diode (“LED”) light source and a light conversion layer disposed separate from and above from the LED light source. The light conversion layer includes a semiconductor nano crystal, converts light emitted from the LED light source to white light and provides the white light to a liquid crystal panel of the LCD.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/269,174, filed on Nov. 12, 2008, which claims priority to KoreanPatent Application No. 10-2008-0004431, filed on Jan. 15, 2008, and allthe benefits accruing therefrom under 35 U.S.C. §119, the contents ofwhich in its entirety are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (“LCD”)device, and more particularly, to a backlight unit for an LCD devicewhich uses a light emitting diode (“LED”) as a light source.

2. Description of the Related Art

LCD devices are a type of display device which forms an image byreceiving external light instead of using self-emitted light to form theimage, as is the case in plasma display panels (“PDPs”) and fieldemission displays (“FEDs”), for example. Thus, the LCD device requires abacklight unit for emitting light at a back surface of the LCD device.

A conventional backlight unit for an LCD device typically uses a coldcathode fluorescent lamp (“CCFL”) as a light source. However, when theCCFL is used as a light source, it is difficult to secure uniformity ofbrightness of light supplied from the CCFL. In addition, color puritydeteriorates as a screen size of the LCD device increases. As a result,a backlight unit which uses three color LEDs as a light source has beendeveloped recently. Since the backlight unit using the three color LEDsas the light source produces an improved color purity, as compared tothe backlight unit using the CCFL, and the backlight unit which uses thethree color LEDs is therefore used in a high quality display device, forexample.

However, the backlight unit which uses the three color LEDs as the lightsource is more costly as compared to the backlight unit which uses theCCFL as the light source. To mitigate this problem, a white LED whichemits light by changing a light output from a single color LED chip to awhite light has been proposed. However, although using the white LED isnot as expensive as using the three color LEDs, a color purity and acolor reproducibility is reduced, as compared to a color purity andcolor reproducibility of an LCD device including the three color LEDs.Accordingly, various attempts for developing a light source which hasimproved color purity and color reproducibility while maintaining pricecompetitiveness in comparison with other light sources, have been made.

BRIEF SUMMARY OF THE INVENTION

To solve at least the abovementioned shortfalls and/or problems, anexemplary embodiment of the present invention provides a backlight unitfor a liquid crystal display (“LCD”) device which uses a light emittingdiode (“LED”) as a light source.

According to an exemplary embodiment of the present invention, abacklight unit for an LCD device includes an LED light source and alight conversion layer. The LCD device includes a liquid crystal panel,and the light conversion layer is disposed separate from the lightemitting diode light source between the liquid crystal panel and thelight emitting diode light source. The light conversion layer includes asemiconductor nano crystal, and the light conversion layer convertslight emitted from the light emitting diode light source to white lightand provides the white light to the liquid crystal panel.

A diffusion panel is provided between the light conversion layer and theliquid crystal panel or, alternatively, between the LED light source andthe light conversion layer.

The light conversion layer is manufactured by coating the semiconductornano crystal onto a transparent substrate or, alternatively, bydistributing the semiconductor nano crystal in a film type material anddistributing the film type material into a transparent composite.Further, the light conversion layer may be manufactured by coating thesemiconductor nano crystal onto the diffusion panel.

The light conversion layer comprises a plurality of layers. In thiscase, the plurality of layers are separated from one another and a blanklayer is formed therebetween.

The LED light source may be disposed at a peripheral side of the lightconversion layer. In this case, a light guide panel is disposed betweenthe light emitting diode light source and the light conversion layer,and the light guide panel guides the light emitted from the LED lightsource to the light conversion layer.

The LED light source emits a blue light or, alternatively, anultraviolet light.

According to an alternative exemplary embodiment of the presentinvention, an LCD device includes an LED light source, a lightconversion layer disposed separate from and above the LED light source,and a liquid crystal panel disposed above the light conversion layer.

The light conversion layer includes a semiconductor nano crystal, thelight conversion layer converts light emitted from the LED light sourceto white light, and the liquid crystal panel forms an image using thewhite light.

The LCD device may further include a diffusion panel disposed betweenthe light conversion layer and the liquid crystal panel or,alternatively, a diffusion panel disposed between the LED light sourceand the light conversion layer.

The LED light source may be disposed at a peripheral side of the lightconversion layer, and emits a blue light or an ultraviolet light.

The liquid crystal panel includes a liquid crystal layer, and a colorfilter disposed adjacent to the liquid crystal layer. The color filterreceives the white light and forms an image having a predetermined colorusing the white light.

According to another alternative exemplary embodiment of the presentinvention, a backlight unit for an LCD device includes an LED lightsource and a light conversion diffusion layer disposed separate from theLED light source between the liquid crystal panel and the LED lightsource. The light conversion diffusion layer includes a semiconductornano crystal, and the light conversion diffusion layer converts lightemitted from the LED light source to white light and provides the whitelight to the liquid crystal panel.

The light conversion diffusion layer is manufactured by distributing thesemiconductor nano crystal in a film type material in a transparentcomposite including a light diffusion material.

The LED light source is disposed at a peripheral side of the lightconversion diffusion layer.

The backlight unit may further include a light guide panel disposedbetween the LED light source and the light conversion diffusion layer,and the light guide panel may guide the light emitted from the LED lightsource to the light conversion diffusion layer.

The light conversion diffusion layer may include a first layer and asecond layer. The first layer has an energy light emission wavelengthless than an energy light emission wavelength of the second layer, andthe first layer is disposed in the light conversion layer closer to theLED light source than the second layer.

According to yet another alternative exemplary embodiment of the presentinvention, an LCD device comprises an LED light source, a lightconversion diffusion layer disposed separate from and above the LEDlight source, and a liquid crystal panel disposed above the lightconversion diffusion layer. The light conversion diffusion layerincludes a semiconductor nano crystal, the light conversion diffusionlayer converts light emitted from the LED light source to white light,and the liquid crystal panel forms an image using the white light.

The LED light source may be disposed at a peripheral side of the lightconversion diffusion layer and emits a blue light or an ultravioletlight.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will become more readily apparent by describing in furtherdetail exemplary embodiments thereof with reference to the accompanyingdrawings, in which:

FIG. 1 is a partial cross-sectional view of a liquid crystal display(“LCD”) device according to an exemplary embodiment of the presentinvention;

FIG. 2 is a partial cross-sectional view of an LCD device according toan alternative exemplary embodiment of the present invention;

FIG. 3 is a partial cross-sectional view of an LCD device according toanother alternative exemplary embodiment of the present invention; and

FIG. 4 is a partial cross-sectional view of an LCD device according toyet another alternative exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like reference numerals refer to like elements throughout.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.

It will be understood that although the terms “first,” “second,” “third”etc. may be used herein to describe various elements, components,regions, layers and/or sections, these elements, components, regions,layers and/or sections should not be limited by these terms. These termsare only used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of the present invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including,” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components and/or groupsthereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top” may be used herein to describe one element's relationship to otherelements as illustrated in the Figures. It will be understood thatrelative terms are intended to encompass different orientations of thedevice in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on the “upper” side of the other elements. The exemplary term“lower” can, therefore, encompass both an orientation of “lower” and“upper,” depending upon the particular orientation of the figure.Similarly, if the device in one of the figures were turned over,elements described as “below” or “beneath” other elements would then beoriented “above” the other elements. The exemplary terms “below” or“beneath” can, therefore, encompass both an orientation of above andbelow.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present invention belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning which isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments of the present invention are described herein withreference to cross section illustrations which are schematicillustrations of idealized embodiments of the present invention. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, embodiments of the present invention should not beconstrued as limited to the particular shapes of regions illustratedherein but are to include deviations in shapes which result, forexample, from manufacturing. For example, a region illustrated ordescribed as flat may, typically, have rough and/or nonlinear features.Moreover, sharp angles which are illustrated may be rounded. Thus, theregions illustrated in the figures are schematic in nature and theirshapes are not intended to illustrate the precise shape of a region andare not intended to limit the scope of the present invention.

Hereinafter, exemplary embodiments of the present invention will bedescribed in further detail with reference to the accompanying drawings.

FIG. 1 is a partial cross-sectional view of a backlight unit accordingto an exemplary embodiment of the present invention and a liquid crystaldisplay (“LCD”) device including the backlight unit. Referring to FIG.1, an LCD device includes a backlight unit 100 and a liquid crystalpanel 500 which displays an image of a predetermined color using whitelight emitted from the backlight unit 100.

The backlight unit 100 includes a light emitting diode (“LED”) lightsource 110, and a light conversion layer 120 which converts lightemitted from the LED light source 110 to white light. The LED lightsource 110 includes a plurality of LED chips (not shown) which emitslight having a predetermined wavelength. In an exemplary embodiment, theLED light source 110 is an LED light source 110 which emits blue light,but alternative exemplary embodiments are not limited thereto. Forexample, the LED light source 110 according to an alternative exemplaryembodiment may be an LED light source 110 which emits an ultravioletlight, for example.

In an exemplary embodiment of the present invention, the lightconversion layer 120 is spaced apart from the LED light source 110 by apredetermined distance, and changes, e.g., converts, light emitted fromthe LED light source 110 to white light and emits the white light towardthe liquid crystal panel 500. The light conversion layer 120 is formedof semiconductor nano crystal. As a result, the light conversion layerprovides advantages of, but not limited to, substantially improved colorreproducibility and color purity.

In an exemplary embodiment of the present invention, the semiconductornano crystal can be formed of at least one of a group II-VI compoundsemiconductor material, a group III-V compound semiconductor material ora group IV semiconductor material. Specifically, the group II-VIcompound semiconductor material, group III-V compound semiconductormaterial and group IV semiconductor material includes, for example,HgTe, HgSe, HgS, CdTe, CdSe, Cds, ZnTe, ZnSe, ZnS, GaN, GaP, InN, InP,InAs, Si and Ge, but alternative exemplary embodiments are not limitedthereto. Rather, these materials are examples of a material which may beused to form the semiconductor nano crystal. Therefore, various othersemiconductor materials may be used for the light conversion layer 120in alternative exemplary embodiments of the present invention. Further,the light conversion layer 120 may be manufactured by coating thesemiconductor nano crystal onto a transparent substrate (not shown) or,alternatively, by distributing a film form in which the semiconductornano crystal is distributed onto a transparent composite.

In addition, the light conversion layer 120 according to an alternativeexemplary embodiment may be formed to include a plurality of layers. Inthis case, the layers are disposed such that a layer has a lightemission wavelength having a lower energy, that is, a longer wavelength,as the layer is located proximate to, e.g., closer to, the LED lightsource 110. For example, when the LED light source 110 is a blue LEDlight source, the plurality of layers may have an arrangement structureof the LED light source 110—a red light conversion layer—a green lightconversion layer. Also, the plurality of layers forming the lightconversion layer 120 may have the following arrangement structure. Forexample, the plurality of layers may have an arrangement structure ofthe LED light source 110—a red light conversion layer—a green lightconversion layer—a red light conversion layer—a green light conversionlayer. Also, the plurality of layers may have another arrangementstructure of the LED light source 110—a red light conversion layer—anorange light conversion layer—a yellow light conversion layer—a greenlight conversion layer. Also, the plurality of layers may have anotherarrangement structure of the LED light source 110—a red+yellow lightconversion layer—a green+orange light conversion layer. Theabove-described arrangement structures of the plurality of layersforming the light conversion layer 120 are exemplarily described sothat, in the present embodiment, a variety of arrangement structures ofthe plurality of layers forming the light conversion layer 120 may beavailable in addition to the above-described arrangement structures.Also, when the light conversion layer 120 is formed of a plurality oflayers, the plurality of layers may be separated a predetermineddistance from one another and a blank layer may be arrangedtherebetween. Accordingly, as the plurality of layers are separated fromone another, energy transfer can be prevented.

When light emitted from the LED light source 110 passes through thelight conversion layer 120 formed of the semiconductor nano crystal,white light mixed with blue light, green light and red light isproduced. Further, the blue light, the green light and the red light arecontrolled, e.g., are maintained to have a desired ratio thereof, bychanging a composition and/or a size of the semiconductor nano crystalwhich forms the light conversion layer 120. Accordingly, a white lighthaving substantially improved color reproducibility and color purity isthereby obtained in an exemplary embodiment of the present invention.

Still referring to FIG. 1, an LCD device according to an exemplaryembodiment of the present invention further includes a diffusion panel130 disposed between the light conversion layer 120 and the liquidcrystal panel 500. The diffusion panel 130 diffuses and emits the whitelight output from the light conversion layer 120. Thus, the white lightpassing through the diffusion panel 130 has a substantially improveduniformity. As shown in FIG. 1, the light conversion layer 120 contactsthe diffusion panel 130, e.g., is disposed directly on the diffusionpanel 130, but alternative exemplary embodiments of the presentinvention are not limited thereto. In an alternative exemplaryembodiment, for example, the light conversion layer 120 may be separatedfrom the diffusion panel 130, e.g., not disposed directly thereon.

As described above, the light conversion layer 120 may be manufacturedby coating the semiconductor nano crystal onto a transparent substrateor, alternatively, by using a film-type material in which thesemiconductor nano crystal is distributed in a transparent composite. Inyet another alternative exemplary embodiment, the light conversion layer120 may be manufactured by coating the semiconductor nano crystal ontothe diffusion panel 130.

A collimating system 140 is provided between the diffusion panel 130 andthe liquid crystal panel 500, as shown in FIG. 1. The collimating system140 condenses the white light output from the diffusion panel 130 to besupplied to the liquid crystal panel 500.

The white light emitted from the backlight unit 100 including the LEDlight source 110 and the light conversion layer 120 is supplied to theliquid crystal panel 500 and is therefore incident thereon. Thus, theliquid crystal panel 500 displays an image having a predetermined colorwith the white light output from the backlight unit 100.

The liquid crystal panel 500 of an LCD device according to an exemplaryembodiment includes a first polarized panel 501, a liquid crystal layer502, a second polarized panel 503 and a color filter 504. In anexemplary embodiment, the first polarized panel 501, the liquid crystallayer 502, the second polarized panel 503 and the color filter 504 aresequentially arranged as illustrated in FIG. 1. As a result, the whitelight output from the backlight unit 100 passes through the firstpolarized panel 501, the liquid crystal layer 502, and the secondpolarized panel 503 and is thereafter incident on the color filter 504,thus forming the image having the predetermined color.

FIG. 2 is a partial cross-sectional view of a backlight unit accordingto an alternative exemplary embodiment of the present invention and anLCD device including the backlight unit. In FIG. 2, the same referencecharacters refer to the same or like components of an LCD devicedescribed above with respect the exemplary embodiment shown in FIG. 1,and any repetitive detailed description thereof has been omitted. Thus,in the following description, only differences from the above-describedexemplary embodiment will be described.

Referring now to FIG. 2, a backlight unit 200 according to an exemplaryembodiment includes an LED light source 210 and a light conversion layer220 disposed separate from the LED light source 210. As described ingreater detail above with reference to FIG. 1, the light conversionlayer 220 converts light output from the LED light source 210 to whitelight. Further, the LED light source 210 according to an exemplaryembodiment includes an LED light source 210 which emits blue light or,alternatively, an LED light source 210 which emits ultraviolet light.The light conversion layer 220 according to an exemplary embodiment isformed of a semiconductor nano crystal, as described in greater detailabove.

The light conversion layer 220 according to an alternative exemplaryembodiment may include more than on layer, e.g., may include a pluralityof layers. In this case, the plurality of layers may have a variety ofarrangement structures as described above. Also, when the lightconversion layer 220 has a plurality of layers, the layers may beseparated a predetermined distance from one another and a blank layermay be arranged therebetween.

In an exemplary embodiment of the present invention, a diffusion panel230 is provided between the LED light source 210 and the lightconversion layer 220, as shown in FIG. 2. Light passing through thediffusion panel 230 is incident on the light conversion layer 220 and istherein changed to white light. In the exemplary embodiment of thepresent invention shown in FIG. 2, the diffusion panel 230 contacts thelight conversion layer 220, e.g., the diffusion panel 230 is disposeddirectly on the light conversion layer 220, but alternative exemplaryembodiments of the present invention are not limited thereto. Forexample, the diffusion panel 230 may be separated from the lightconversion layer 220 by a predetermined distance.

A collimating system 240 which condenses the white light output towardthe liquid crystal panel 500 from the light conversion layer 220 isprovided between the light conversion layer 220 and the liquid crystalpanel 500. Thus, the liquid crystal panel 500 forms an image having apredetermined color using the white light output from the backlight unit200, as described in greater detail above.

FIG. 3 is a partial cross-sectional view of a backlight unit accordingto another exemplary embodiment of the present invention and an LCDdevice including the backlight unit. In FIG. 3, the same referencecharacters refer to the same or like components of an LCD devicedescribed above with respect to the exemplary embodiments shown in FIGS.1 and 2, and any repetitive detailed description thereof has beenomitted. Thus, in the following description, only differences from theabove-described exemplary embodiments will be described.

Referring to FIG. 3, a backlight unit 300 according to an exemplaryembodiment includes an LED light source 310 and a light conversiondiffusion layer 325 disposed separate from the LED light source 310. Inan exemplary embodiment of the present invention, the LED light source310 can is an LED light source 310 which emits blue light or,alternatively, may be an LED light source 310 which emits ultravioletlight, as described above in greater detail with reference to FIG. 1.The light conversion diffusion layer 325 functions as the lightconversion layer 120 (FIG. 1) or the light conversion layer 220 (FIG.2), as well as the diffusion layer 130 (FIG. 1) or the diffusion layer230 (FIG. 2). Thus, the light conversion diffusion layer 325 diffuseslight outputted from the LED light source 310 and also converts thelight outputted from the LED light source 310 to white light, andthereafter emits the white light toward the liquid crystal panel 500.The light conversion diffusion layer 325 according to an exemplaryembodiment of the present invention includes a semiconductor nanocrystal, as described in greater detail above with reference to FIG. 1.In addition, the light conversion diffusion layer 325 may bemanufactured as a film type material in which the semiconductor nanocrystal is distributed in a transparent composite, including a lightdiffusion material.

The semiconductor nano crystal according to an exemplary embodiment maybe formed of at least one of a group II-VI compound semiconductormaterial, a group III-V compound semiconductor material, and a group IVsemiconductor element. The group II-VI compound semiconductor material,group III-V compound semiconductor material, and group IV semiconductormaterial include HgTe, HgSe, HgS, CdTe, CdSe, Cds, ZnTe, ZnSe, ZnS, GaN,GaP, InN, InP, InAs, Si, and Ge. It will be noted that alternativeexemplary embodiments are not limited to the abovementioned materials.Rather, the abovementioned materials are merely examples of materialswhich may be used in forming the semiconductor nano crystal, and variousother semiconductor materials can be used for the light conversiondiffusion layer 325.

In addition, the light conversion diffusion layer 325 according to anexemplary embodiment may be formed to include a plurality of layers. Inthis case, the layers are disposed such that a layer has a lightemission wavelength having a lower energy, that is, a longer wavelength,as the layer is located proximate to, e.g., closer to, the LED lightsource 310. For example, when the LED light source 310 is a blue LEDlight source, the plurality of layers may have an arrangement structureof the LED light source 310—a red light conversion layer—a green lightconversion layer. Also, the plurality of layers forming the lightconversion diffusion layer 325 may have the following arrangementstructure. For example, the plurality of layers may have an arrangementstructure of the LED light source 310—a red light conversion layer—agreen light conversion layer—a red light conversion layer—a green lightconversion layer. Also, the plurality of layers may have anotherarrangement structure of the LED light source 310—a red light conversionlayer—an orange light conversion layer—a yellow light conversion layer—agreen light conversion layer. Also, the plurality of layers may haveanother arrangement structure of the LED light source 310—a red+yellowlight conversion layer—a green+orange light conversion layer. Theabove-described arrangement structures of the plurality of layersforming the light conversion diffusion layer 325 are exemplarilydescribed so that, in the present embodiment, a variety of arrangementstructures of the plurality of layers forming the light conversiondiffusion layer 325 may be available in addition to the above-describedarrangement structures. Also, when the light conversion diffusion layer325 is formed of a plurality of layers, the plurality of layers may beseparated a predetermined distance from one another and a blank layermay be arranged therebetween.

A collimating system 340 for condensing the white light output from thelight conversion diffusion layer 325 to the liquid crystal panel 500 isdisposed between the light conversion diffusion layer 325 and the liquidcrystal panel 500. Therefore, as described above in greater detail withreference to FIG. 1, the liquid crystal panel 500 forms an image havinga predetermined color using the white light emitted from the backlightunit 300.

FIG. 4 is a partial cross-sectional view of a backlight unit accordingto still another alternative exemplary embodiment of the presentinvention and an LCD device including the backlight unit. In FIG. 4, thesame reference characters refer to the same or like components of an LCDdevice described herein with respect to the exemplary embodiments shownin FIGS. 1-3, and any repetitive detailed description thereof has beenomitted. Thus, in the following description, only differences from theabove-described exemplary embodiments will be described.

Referring to FIG. 4, a backlight unit 400 according to an exemplaryembodiment of the present invention includes an LED light source 410 anda light conversion layer 420 disposed separate from the LED light source410. In an exemplary embodiment, the LED light source 410 is disposedunder and at a side of the light conversion layer 420, rather thandirectly under the light conversion layer 420 (as was the case inalternative exemplary embodiments described above with reference toFIGS. 1-3, for example). Thus, the LED light source 410 is disposed tothe side of and under the light conversion layer 420, as shown in FIG.4. In an exemplary embodiment, the LED light source 410 is an LED lightsource 410 which emits blue light or, alternatively, an LED light source410 which emits an ultraviolet light.

A light guide panel 415 is provided in an optical path between the LEDlight source 410 and the light conversion layer 420. More specifically,light guide panel 415 is disposed under, e.g., directly under, the lightconversion layer 420, as shown in FIG. 4. The light guide panel 415guides light emitted from the LED light source 410, disposed at a sideof the light guide panel 415, toward the light conversion layer 420.Accordingly, the light emitted from the LED light source 410 passesthrough the light guide panel 415 and is thereafter incident on thelight conversion layer 420. The light incident on the light conversionlayer 420 is changed to white light as it passes through the lightconversion layer 420.

In an exemplary embodiment of the present invention, the lightconversion layer 420 is formed of a semiconductor nano crystal, asdescribed in greater detail above. The light conversion layer 420according to an alternative exemplary embodiment can be formed toinclude a plurality of layers. In this case, the plurality of layers mayhave a variety of arrangement structures as described above. Also, whenthe light conversion layer 420 has a plurality of layers, the layers maybe separated a predetermined distance from one another and a blank layermay be arranged therebetween.

A diffusion panel 430 is disposed between the light conversion layer 420and the liquid crystal panel 500. The diffusion panel 430 diffuses andemits the white light output from the light conversion layer 420 tosubstantially improve a uniformity of the white light. In the exemplaryembodiment of the present invention shown in FIG. 4, the lightconversion layer 420 contacts the diffusion panel 430, e.g., is disposeddirectly on the diffusion panel 430, but alternative exemplaryembodiments of the present invention are not limited thereto. In analternative exemplary embodiment, for example, the light conversionlayer 420 may be disposed separate from the diffusion panel 430, e.g.,not directly on the diffusion panel 430.

The light conversion layer 420 may be manufactured by coating thesemiconductor nano crystal onto a transparent substrate or,alternatively, in a film type material in which the semiconductor nanocrystal is distributed in a transparent composite, as described ingreater detail above. Alternatively, the light conversion layer 420 maybe manufactured by coating the semiconductor nano crystal onto thediffusion panel 430.

In an exemplary embodiment of the present invention, a collimatingsystem 440 is disposed between the diffusion panel 430 and the liquidcrystal panel 500. The collimating system 140 condenses the white lightoutput from the diffusion panel 130 toward the liquid crystal panel 500.Thereafter, the liquid crystal panel 500 forms an image having apredetermined color using the white light emitted from the backlightunit 400, as described in greater detail above.

In the exemplary embodiment illustrated in FIG. 4, the diffusion panel430 is shown as being disposed between the light conversion layer 420and the liquid crystal panel 500, but alternative exemplary embodimentsare not limited thereto. For example, the diffusion panel 430 may bedisposed between the LED light source 410 and the light conversion layer420, as described in greater detail above with reference to FIG. 2.Also, in an alternative exemplary embodiment, a light conversiondiffusion layer 325 (FIG. 3) may be provided instead of the lightconversion layer 410 and the diffusion panel 430. Further, the lightconversion diffusion layer 325 may be manufactured by distributing thesemiconductor nano crystal in a transparent composite including a lightdiffusion material. In this case, the light emitted from the LED lightsource 410 is incident on the light conversion diffusion layer 235 viathe light guide panel 415. Thus, the light incident on the lightconversion diffusion layer is diffused and changed to white light whilepassing through the light conversion diffusion layer, and is thereafteremitted to the liquid crystal panel 500 to form the image having thepredetermined color using the white light emitted from the backlightunit 400.

According exemplary embodiments of the present invention as describedherein, color reproducibility and color purity of a backlight unit aresubstantially improved, since a light conversion layer is formed of asemiconductor nano crystal. Since the light conversion layer or,alternatively, a light conversion diffusion layer, is disposed separatefrom an LED light source, operating characteristics of the lightconversion layer (or of light conversion diffusion layer) are notdegraded due to heat generated from LED chips, for example. Also, thelight conversion layer formed of the semiconductor nano crystal may bemanufactured as a separate film type material, and a manufacturingprocess of the backlight unit is thereby substantially simplified.

The present invention should not be construed as being limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the concept of the present invention tothose skilled in the art.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit or scopeof the present invention as defined by the following claims.

1. A backlight unit for a liquid crystal display device including aliquid crystal panel, the backlight unit comprising: a light emittingdiode light source; and a light conversion layer disposed separate fromthe light emitting diode light source between the liquid crystal paneland the light emitting diode light source, wherein the light conversionlayer comprises a semiconductor nano crystal, and the light conversionlayer converts light emitted from the light emitting diode light sourceto white light and provides the white light to the liquid crystal panel.2. The backlight unit of claim 1, further comprising one of a diffusionpanel disposed between the light conversion layer and the liquid crystalpanel and a diffusion panel disposed between the light emitting diodelight source and the light conversion layer.
 3. The backlight unit ofclaim 1, wherein the light conversion layer is manufactured by coatingthe semiconductor nano crystal onto a transparent substrate.
 4. Thebacklight unit of claim 1, wherein the light conversion layer ismanufactured by distributing the semiconductor nano crystal in a filmtype material and distributing the film type material into a transparentcomposite.
 5. The backlight unit of claim 2, wherein the lightconversion layer is manufactured by coating the semiconductor nanocrystal onto the diffusion panel.
 6. The backlight unit of claim 1,wherein the light conversion layer comprises a plurality of layers. 7.The backlight unit of claim 6, wherein the plurality of layers aredisposed such that a layer has a light emission wavelength having alower energy as the layer is located closer to the LED light source. 8.The backlight unit of claim 6, wherein the plurality of layers areseparated from one another and a blank layer is formed therebetween. 9.The backlight unit of claim 1, wherein the light emitting diode lightsource is disposed at a side of the light conversion layer.
 10. Thebacklight unit of claim 9, further comprising a light guide paneldisposed between the light emitting diode light source and the lightconversion layer, wherein the light guide panel guides the light emittedfrom the light emitting diode light source to the light conversionlayer.
 11. The backlight unit of claim 1, wherein the light emittingdiode light source emits one of a blue light and an ultraviolet light.12. A liquid crystal display device comprising: a light emitting diodelight source; a light conversion layer disposed separate from and abovethe light emitting diode light source; and a liquid crystal paneldisposed above the light conversion layer, wherein the light conversionlayer comprises a semiconductor nano crystal, the light conversion layerconverts light emitted from the light emitting diode light source towhite light, and the liquid crystal panel forms an image using the whitelight.
 13. The liquid crystal display device of claim 12, furthercomprising one of a diffusion panel disposed between the lightconversion layer and the liquid crystal panel and a diffusion paneldisposed between the light emitting diode light source and the lightconversion layer.
 14. The liquid crystal display device of claim 12,wherein the light emitting diode light source is disposed at aperipheral side of the light conversion layer.
 15. The liquid crystaldisplay device of claim 12, wherein the light emitting diode lightsource emits one of a blue light and an ultraviolet light.
 16. Theliquid crystal display device of claim 12, wherein the liquid crystalpanel comprises: a liquid crystal layer; and a color filter disposedadjacent to the liquid crystal layer, wherein the color filter receivesthe white light and forms an image having a predetermined color usingthe white light.
 17. A backlight unit for a liquid crystal displaydevice including a liquid crystal panel, the backlight unit comprising:a light emitting diode light source; and a light conversion diffusionlayer disposed separate from the light emitting diode light sourcebetween the liquid crystal panel and the light emitting diode lightsource, wherein the light conversion diffusion layer comprises asemiconductor nano crystal, and the light conversion diffusion layerconverts light emitted from the light emitting diode light source towhite light and provides the white light to the liquid crystal panel.18. The backlight unit of claim 17, wherein the light conversiondiffusion layer is manufactured by distributing the semiconductor nanocrystal in a film type material in a transparent composite including alight diffusion material.
 19. The backlight unit of claim 17, whereinthe light emitting diode light source is disposed at a peripheral sideof the light conversion diffusion layer.
 20. The backlight unit of claim19, further comprising a light guide panel disposed between the lightemitting diode light source and the light conversion diffusion layer,wherein the light guide panel guides the light emitted from the lightemitting diode light source to the light conversion diffusion layer.